This invention relates generally to thermoelectric cooler temperature control, and more particularly to a method and apparatus for monitoring and stabilizing temperature of a heat-generating system using a thermoelectric cooler.
A Thermoelectric Cooler (TEC) is a cooling device that uses the Peltier effect for heat transfer. The Peltier effect occurs whenever electrical current flows through two dissimilar conductors. The two dissimilar conductors are connected through two junctions; one releases heat, and the other one absorbs heat.
Referring to FIG. 1, a TEC 15 can be constructed by soldering a semiconductor pellet 13 to electrically conductive material, typically plated copper (11 and 12), on each side of the pellet. The two ends of semiconductor pellet 13 are connected to a DC power supply 112 through a copper connection path 19. With this configuration, the first conductor of the two dissimilar conductors is semiconductor pellet 13, and the second conductor includes the plated copper (11 and 12) and copper connection path 19.
The Peltier effect is created by charge carriers that carry heat from one side of the pellet 13 to the other. For example, if an N-type semiconductor material is used to fabricate pellet 13, electrons will be the charge carriers. With a DC voltage source connected, electrons will be repelled by a negative pole 111 of power supply 112, and attracted by a positive pole 110 of the supply. The movement of the electrons flows in a counter-clockwise direction, as shown in FIG. 1. With the electrons flowing through the N-type material from bottom to top, heat is absorbed at the bottom junction and actively transferred to the top junction, and is effectively pumped by the electrons through semiconductor pellet 13. The heat moves in the direction of electron movement throughout the circuit.
To monitor and stabilize temperature in a system using a TEC, it is generally required that a thermistor, or some other temperature monitoring device with absolute accuracy, be mounted on a xe2x80x9ccoldxe2x80x9d side, i.e., bottom plated copper 12, of the TEC. The output from the device controls a servo loop (not shown) for stabilizing the temperature.
With typical applications of these devices, the cold side is generally enclosed in a heat-generating system. Therefore, mounting of a thermistor on the cold side has several drawbacks. For example, installing the thermistor on the cold side may require additional manufacturing processes that add to the final assembled cost of the system. Moreover, the reliability of the system and the yield can decrease due to the additional manufacturing processes and the possibility of failure of the monitoring device.
The invention relates to a method and apparatus for monitoring and stabilizing temperature in a heat-generating system using a thermoelectric cooler.
In a general aspect, the invention features a method and apparatus for temperature control using the Seebeck effect of a thermoelectric cooler, the method and apparatus including a current source that generates current; a thermoelectric cooler having a first end and a second end, both connecting to the current source; and a control circuit, which monitors voltage difference across the two ends of the thermoelectric cooler and controls the current source according to the voltage difference.
In another aspect, the invention features a method and apparatus that controls a temperature delta between the two ends of the thermoelectric cooler from the voltage difference. The voltage difference is used to derive the temperature delta and to calculate the polarity and magnitude of current that will bring the cooler to a desired temperature point. The control circuit activates the current source for a fixed duration of time, turns off the current source for measuring the voltage difference, and re-activates the current source according to the calculated current when the voltage difference after measuring the voltage difference. The control operations performed by the current source includes the operations of activation, deactivation, and re-activation of the current source, the operations being performed in a continuous cycle to maintain a substantially constant temperature delta across the two ends of the thermoelectric cooler.
In another aspect, the invention further features an external monitoring device mounted on a first end of the thermoelectric cooler for measuring an absolute temperature of the first end. The temperature of a second end of the thermoelectric cooler is stabilized based on an absolute temperature of the first end and temperature difference between the two ends.
The invention can be applied to any devices that use thermoelectric coolers for temperature control; for examples, LASER modules built by Nortel Networks, or tunable optical filters.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.